The invention relates to the field of semiconductor processing. More specifically, the invention relates to forming a nitrogen containing group III-arsenide compound semiconductor using ammonia as a precursor.
Long wavelength lasers, lasers that emit light in wavelengths between 1.3 micrometers and 1.6 micrometers, are highly desirable for telecommunication system use because at these xe2x80x9ctelecom wavelengthsxe2x80x9d, a xe2x80x9cwavelength windowxe2x80x9d exists where light absorption in optical fibers is minimized. As telecommunications increasingly rely on optical signal transmission, these long wavelength lasers have become increasingly important.
Most optoelectronic components in the telecom wavelength range are grown on InP substrates. An InP substrate is preferred because the substrate easily lattice matches with high indium composition InGaAs films used in the fabrication of devices that emit 1.3-1.6 micron wavelength light. However, high substrate costs and low device yields makes InP-based optoelectronic devices rather expensive. Devices based on GaAs substrates would be much cheaper, but the difference in lattice constant normally prevents the growth of InGaAs with high In compositions (xcx9c50% indium mole fraction is preferred to achieve relevant telecom outputs) on GaAs substrate.
The bandgap in a semiconductor laser determines the frequency of light output by a semiconductor laser. Recently it has been demonstrated that by incorporating small amounts (fraction of a percent to a few percent) of nitrogen into the InGaAs film, the band gap of InGaAs alloys grown on GaAs substrate can be reduced thereby shifting the light emitted by the resulting devices to longer wavelengths. Indium Gallium Arsenide Nitride alloys have been found to be excellent semiconductor materials for fabricating the active region of VCSELS or other long-wavelength optoelectronic devices (e.g. edge-emitting laser, photodetectors or solar cells). Using elementary nitrogen as a group V source and a Molecular Beam Epitaxy (MBE) process, several groups have fabricated InGaAsN based lasers that output 1.3 micrometer wavelength light. See, M. Kondow et al., Jpn. J. Appl. Phys., Vol. 35, 1273 (1996) and M. Kondow, S. Natatsuka, T. Kitatani, Y. Yazawa, and M. Okai, Electron. Lett. 32, 2244 (1996). However, MBE is a slow growth technique and therefore not well suited to mass production of high volume optoelectronic devices such as VCSELs, egde-emitting lasers or solar cells.
Metal Organic Chemical Vapor Deposition (MOCVD) is a suitable technique for volume production of InGaAsN lasers. However, the high growth temperatures and surface chemistry of MOCVD results in inefficient incorporation of elemental nitrogen (N) in the InGaAsN material. To increase the incorporation efficiency of Nitrogen in the InGaAsN, the Nitrogen is typically introduced in a dimethylhydrazine (DMHy) form as described in J. Koch, F. Hohnsdorf, W. Stolz, Journal of Electronic Materials, Vol. 29, 165 (2000) and A. Ougazzaden et al., Appl. Phys. Lett. 70, 2861 (1997) which are hereby incorporated by reference. Large oversupplies of DMHy are used to achieve sufficient amounts of nitrogen in the InGaAsN structure.
The use of large quantities of DMHy as a nitrogen source has two major disadvantages. The first disadvantage is high cost. DMHy is expensive, current costs for 100 grams of DMHy is approximately $5000. A second disadvantage of using DMHy as a Nitrogen source is the relatively high impurity levels that often exist in commercially available DMHy. High impurity levels are possibly one reason why MOCVD grown InGaAsN films are often inferior to MBE grown films.
Thus a better source of Nitrogen for forming InGaAsN structures is needed.